Presently, there are few if any commercially available sorbent polymers that have strong hydrogen bond acidic properties. Moreover, there are none that have glass to rubber transition temperatures below room temperature. None of the conventional gas chromatographic stationary phases are strong hydrogen-bond acids, and those that are more modest hydrogen-bond acids (docosanol, sorbitol, and diglycerol) are not polymers.
In the paper FLUORALCOHOL- AND FLUOROPHENOL-CONTAINING POLYMERS FOR ACOUSTIC WAVE AND OPTICAL SENSORS, J W Grate, S N Kangrove, S J Patrash, B M Wise, ECS Meeting Abstracts Volume 96-1, April 1996, it is reported that experimental chemical sensors have been made using hydrogen bond acidic polymers as the sorbent material to collect and concentrate hydrogen bond basic vapors on the sensor surface. For example, an oligomeric epoxy dubbed "fluoropolyol" has been used for the detection of basic vapors such as organophoshorus compounds using surface acoustic wave (SAW) sensors, a result attributed to hydrogen bonding interactions. Fluropolyol was originally developed at the Naval Research Laboratory(NRL) as a component of epoxy paints, and NRL has remained the sole source of this material for sensor studies. Fluoropolyol has also been used in sensor arrays for classifying organophosphorus compounds, and fluoropolyol was used in a smart sensor array system for detecting these compounds as reported in A. W. Snow, L. G. Sprague, R. L. Soulen, J. W. Grate, and H. Wohltjen, Synthesis and evaluation of hexafluorodimethylcarbinol functionalized polymers as microsensor coatings, J. Appl. Poly. Sci., 43 (1991) 1659-1671; J. W. Grate, A. Snow, D. S. Ballantine, H. Wohltjen, M. H. Abraham, R. A. McGill, and P. Sasson, Determination of partition coefficients from surface acoustic wave vapor sensor responses and correlation with gas-liquid chromatographic partition coefficients, Anal. Chem., 60 (1988) 869-875; D. S. Ballantine, S. L. Rose, J. W. Grate, and H. Wohltjen, Correlation of surface acoustic wave device coating responses with solubility properties and chemical structure using pattern recognition, Anal. Chem., 58 (1986) 3058-3066; J. W. Grate, M. Klusty, R. A. McGill, M. H. Abraham, G. Whiting, and J. Andonian-Haftvan, The predominant role of swelling-induced modulus changes of the sorbent phase in determining the responses of polymer-coated surface acoustic wave vapor sensors, Anal. Chem., 64 (1992) 610-624; S. L. Rose-Pehrsson, J. W. Grate, D. S. Ballantine, and P. C. Jurs, Detection of hazardous vapors including mixtures using pattern recognition analysis of responses from surface acoustic wave devices, Anal. Chem., 60 (1988) 2801-2811; and J. W. Grate, S. L. Rose-Pehrsson, D. L. Venezky, M. Klusty, and H. Wohltjen, A smart sensor system for trace organophosphorus and organosulfur vapor detection employing a temperature-controlled array of surface acoustic wave sensors, automated sample preconcentration, and pattern recognition, Anal. Chem., 65 (1993) 1868-1881. Fluoropolyol has also been used as a component of a polymer/phthalocyanine composite Langmuir-Blodgett films on chemiresistor sensors as reported by J. W. Grate, M. Klusty, W. R. Barger, and A. W. Snow, Role of selective sorption in chemiresistor sensors for organophosphorous detection, Anal. Chem., 62 (1990) 1927-1924. The use of fluoropolyol in these and other applications has made it the de facto standard for hydrogen-bond acidic SAW sensor coatings. Fluoropolyol has a glass transtition temperature of 10.degree. C.
Experimental chemical sensors have been made using organic polymers based on poly(styrene) and poly(isoprene) polymer backbones with pendant hexafluoroisopropanol (HFIP) groups, where the HFIP group provides strong hydrogen bond acidic properties as reported by Snow et al. (cited above) and J. W. Barlow, P. E. Cassidy, D. R. Lloyd, C. J. You, Y. Chang, P. C. Wong, and J. Noriyan, Polymer sorbents for phosphorus esters: II. Hydrogen bond driven sorption in fluoro-carbinol substituted polystyrene, Polym. Eng. Sci., 27 (1987) 703-715; Y. Chang, J. Noriyan, D. R. Lloyd, and J. W. Barlow, Polymer sorbents for phosphorus esters: I. Selection of polymers by analog calorimetry, Polym. Eng. Sci., 27 (1987) 693. These materials on SAW devices afforded vapor sensors with high sensitivities to organophosphorus compounds, but both the parent polymers and the HFIP-containing materials were glassy at room temperature. This property limits the vapor diffusion rate in the polymer, resulting in sensors that are slow to respond and recover.
An HFIP-containing polymer based on a polysiloxane backbone has been described and demonstrated to be a good hydrogen-bond acid on the basis of inverse chromatography and linear salvation energy relationship (LSER) studies by M. H. Abraham, J. Andonian-Haftvan, C. M. Du, V. Diart, G. Whiting, J. W. Grate, and R. A. McGill, Hydrogen Bonding. XXIX. The characterisation of fourteen sorbent coatings for chemical microsensors using a new salvation equation, J. Chem. Soc., Perkin Trans. 2, (1995) 369-378. The polysiloxane backbone provides a material with a Tg well below room temperature. However, there are few if any published data on the performance of this material on a chemical sensor, and methods to adjust the physical properties of the material, or to crosslink the material, have not been described. In addition, the synthesis of this polymer requires the use of hexafluoroacetone, an extremely toxic reagent.
Phenolic liquids have been shown to be sorbents with hydrogen bond acidic properties. Specifically, the phenolic liquids were derivatives of bisphenol-A and fluoroalkyl-substituted bisphenol with pendant allyl groups or with pendent propyl groups were reported by M. H. Abraham, I. Hamerton, J. B. Rose, and J. W. Grate, Hydrogen is bonding Part 18. Gas-liquid chromatographic measurements for the design and selection of some hydrogen bond acidic phases suitable for use as coatings on piezoelectric sorption detectors, J. Chem. Soc. Perkin Trans. 2, (1991) 1417-1423. The flourinated bisphenol compounds were significantly more acidic than the bisphenol compounds without the fluorination. However, the bisphenol compounds are in a liquid form that is difficult to deploy as a sensing material. The liquids do not form stable thin film. The liquids have a finite vapor pressure and evaporation (albeit slowly) causes drift in sensor baseline and reductions in sensitivity.
A polymer containing bisphenol units in the backbone (FIG. 1a) has been synthesized. Mathias reported in a short communication in 1993 that a non-fluorinated bisallyl derivative of bisphenol-A (1a) underwent rapid hydrosilylation with 1,1,3,3-tetramethyldisiloxane and 1,1,3,3,5,5-hexamethyltrisiloxane (2) at ice-bath temperature yielding polymers with alternating bisphenol and oligosiloxane units (3), L. J. Mathias, and C. M. Lewis, Unexpectedly Rapid Hydrosilation Polymerization of the Diallyl Derivative of Bisphenol-A and 2,6-Diallylphenol, Macromolecules, 26 (1993) 4070-4071. The reaction was strongly exothermic at ice bath temperatures, with high conversion to polymer in seconds to minutes. The glass transition temperature of this polymer was reported to be -29C. This polymer was not crosslinked. It has not been used as the sorbent phase on a chemical sensor. Although the phenolic hydroxyl groups make this polymer hydrogen bond acidic, it cannot be considered strongly hydrogen bond acidic because the bisphenol units are not fluorinated.
M. H. Abraham, I. Hamerton, J. B. Rose and J. W. Grate, HYDROGEN BONDING PART 18. GAS LIQUID CHROMATOGRAPHIC MEASUREMENTS FOR THE DESIGN AND SELECTION OF SOME HYDROGEN BOND ACIDIC PHASE SUITABLE FOR USE AS COATINGS ON PIEZOELECTRIC SORPTION DETECTORS, J. Chem. Soc. Perkin Trans. 2, (1991) 1417-1423 showed using chromatographic studies of vapor sorption and linear solvation energy relationships (LSERs) that a fluoroalkyl-substituted bisphenol with pendant allyl groups, 1b (FIG. 1b), and a variant with pendent propyl groups, were significantly more acidic than similar compounds without the fluorination, such as 1a. The LSER b-coefficient, which measures hydrogen-bond acidity, was 4.56 for fluorinated 1b, compared to only 2.41 for unfluorinated 1a. Since these coefficients are used in an equation that predicts the logarithm of a partition coefficient, an increase in the b-coefficient of 2 units corresponds to increasing the extent of sorption due to the hydrogen bonding interaction by a factor of 100. Indeed the observed partition coefficients for ethylamine into 1b and 1a were 10,800 and 56, respectively, demonstrating the profound advantage in using the fluorinated material to promote the sorption of basic vapors.
In spite of the clear advantage of the fluroinated bisphenol, none of the prior art taught how a sorbent polymer with a fluorinated bisphenol group could be synthesized. Moreover, it was not known whether a fluorinated bisphenol would have the same reactivity as a non-fluorinated bisphenol under hydrosilylation polymerization conditions at ice bath temperatures.
Thus, before the present invention, hydrogen-bond acidic polymers with low glass to rubber transition temperatures for use in sensor arrays were not readily available. Strongly hydrogen bond acidic or sorbent polymers are needed in arrays for the sensitive detection of basic vapors, or to help discrimnate against basic vapors that may interfere with identification of other vapors of interest. Hence, there is a need for a strongly hydrogen bond acidic or sorbent polymer in a solid phase with a low glass to rubber transition temperature useful as a sorbent exhibiting rapid vapor diffusion.